Dredge cutterheads are used for excavating earthen material that is underwater, such as a riverbed. In general, a dredge cutterhead 1 includes several arms 2 that extend forward from a base ring 3 to a hub 4 (FIG. 21). The arms are spaced about the base ring and formed with a broad spiral about the central axis of the cutterhead. Each arm 2 is provided with a series of spaced apart teeth 5 to dig into the ground. The teeth are composed of adapters or bases 6 that are fixed to the arms, and points 7 that are releasably attached to the bases by locks 8.
In use, the cutterhead is rotated about its central axis to excavate the earthen material. A suction pipe is provided near the ring to remove the dredged material. To excavate the desired swath of ground, the cutterhead is moved side-to-side as well as forward. On account of swells and other movement of the water, the cutterhead also tends to move up and down, and periodically impact the bottom surface. Further difficulties are caused by the operator's inability to see the ground that is being excavated underneath the water; i.e., unlike most other excavating operations, the dredge cutterhead cannot be effectively guided along a path to best suit the terrain to be excavated. In view of the heavy loads and severe environment, the point and base interconnection needs to be stable and secure.
The cutterheads are rotated such that the teeth are driven into and through the ground at a rapid rate. Consequently, considerable power is needed to drive the cutterhead, particularly when excavating in rock. In an effort to minimize the power requirements, dredge points are typically provided with elongate, slender bits for easier penetration of the ground. However, as the bit becomes shorter due to wear, the mounting sections of the points will begin to engage the ground in the cutting operation. The mounting section is wider than the bit and is not shaped for reduced drag. On account of the resulting increased drag the mounting sections impose on the cutterhead, the points are usually changed at this time before the bits are fully worn away.